My dear Hooker

If your Acropera case sh^d. really turn out as you suspect, it would be very curious & would greatly interest me,—especially, as I chanced in another case to speculate on the possibility of such action. Unless wind by agitating slightly the flower would effect this, I sh^d. not believe in it. Wind is, necessary to self fertilisation of Bee Ophrys.—¹ I hope you will look to this. Try, if by any chance by pricking inside of Labellum, whether it be irritable.— How I sh^d. like to see one of the Bulbophyllum or other orchids with irritable Labellum!

I shall be particularly glad to see Acropera, as you kindly propose to send it. From analogy with Epipactis palustris, I sh^d. suspect its use was to direct insects in & out of flower in a different direction.—²

I have seen Odontoglossum & Miltonia: & as you say they have nothing remarkable; except indeed that in Miltonia the caudicle has not usual movements of depression. By the way the mechanism of this movement is rather curious & all lies in the bit of exterior membrane of rostellum, which is removed with gland. It is rather odd that I have not found one accurate or intelligible description of the so-called gland in Ophreæ, & still less in the Vandeæ

Catasetum is too long a story, & would weary you, though it is a pleasure to me to write. You may rely that the ejection of pollinia is special contrivance; & the plant would never set a seed without it; for an insect could never remove pollinia without this action.³ M^r Smith is very partially right about the kind of Elasticity.⁴ The irritation which excites the rupture of rostellum (this rupturing is common to many Orchids) is transmitted along the curled horns, or as I think I shall call them the antennæ. The pollinia are ejected with sticky gland foremost & will surely stick on the head of insect, when it touches tips of the antennæ, which stand over, what seems to be the nectar-receptacle.—

Ever yours | C. Darwin

[HAND] You must let me send Parslow for a Mormodes when open.— I am very curious to see it⁵

P.S. I have again changed my mind & sh^d. be much obliged for 2 or 3 very young buds of any of the Vandeæ   Oncidium w^d be best: for I want to see whether the attachment of caudicle is effected in them as in Spiranthes: if you can send me buds, please do not send them for a week, when I shall have finished with M^r Sowerby & drawings.—⁶

Could you lend me Reichenbach;⁷ I sh^d be very glad to see it; if so please send it by enclosed address.—

You speak of pollen-masses of Acropera not sticking to stigma; this is often or generally the case if you pull straight out of stigma; but if you pull at right angles, as an insect could do in flying away, the elastic part of caudicle is stretched & drawn over the edge of stigmatic cavity, & (though so wonderfully strong in some cases) ruptures.

Most cordial thanks for all your kindness & writing so long a letter. I am glad to hear of your Arctic paper.⁸

Your affect | C. D.